Prostate cancer is a form of cancer that develops in the prostate, a gland in the male reproductive system. Most prostate cancers are slow growing; however, there are cases of aggressive prostate cancers. The cancer cells may metastasize (spread) from the prostate to other parts of the body, particularly the bones and lymph nodes. Prostate cancer may cause pain, difficulty in urinating, problems during sexual intercourse, or erectile dysfunction. Other symptoms can potentially develop during later stages of the disease.
Treatment options for prostate cancer with intent to cure are primarily surgery, radiation therapy, stereotactic radiosurgery, and proton therapy. Other treatments, such as hormonal therapy, chemotherapy, cryosurgery, and high intensity focused ultrasound (HIFU) also exist, although not FDA approved, depending on the clinical scenario and desired outcome.
Radiation therapy has some advantages over surgery: the patient can continue to work during treatment, and does not have as long a recovery period as would occur after surgery. In addition, radiation therapy can cure localized prostate cancer, as can surgery. Prostate cancer is treated with both external and internal radiation therapy, and some men will be treated with both types. Internal radiation therapy, also known as brachytherapy, is a procedure in which radioactive seeds are implanted directly into the prostate to kill the cancer. External radiation therapy typically is given five days a week for a period of six to eight weeks, using a machine that looks much like a regular X-ray machine. The procedure is not painful, and each treatment lasts only a few minutes.
In external beam therapy, several beams are aimed at the tumor, and radiation is thus concentrated at the intersection point of the various beams. This therapy is often combined with the use of flexible balloons, or more rigid objects, to hold healthy tissue away from the target area, thus minimizing the dose to healthy tissue. For example, a rectal balloon can be used to push the rectal wall away from the prostate.
The side effects of external beam radiation therapy tend to be less severe than the side effects of other prostate cancer treatments. However, there is still the possibility of incontinence, erectile dysfunction, rectal damage and the like. One of the important contributors to these side effects is uncertain positioning in daily set-up and as caused by tumor motion. Such uncertainties can be caused by internal movements (for example, respiration, bladder filling, peristaltic motions of the gastrointestinal tract, rectal gas and the like) and movement of external skin marks relative to the tumor position.
In fact, researchers report the intrinsic motion of the prostate gland can be as much as 5 mm in the anterior to posterior direction due to rectal peristalsis. This has led to an additional 3 to 5 mm margin being added to the radiation field to account for prostate motion, along with 2 to 5 mm for setup error and dose buildup each, for a total margin of 10 to 15 mm to allow for the dose to reach 100% of the prescribed dose. If internal prostate motion is not addressed, it can lead to under-dosing of the target, and/or over-dosing of healthy surrounding tissues.
External patient positioning systems attempt to minimize anatomical variations by providing a secure and reproducible scaffolding, allowing the patient to comfortably maintain a relatively stable external position. However, external positioning systems cannot compensate for daily internal anatomical variations and organ movement due to breathing, rectal peristalsis, and rectal gas, which have been shown to be the major component of variation in target localization.
One way of minimizing the effects of such internal motions is to compress the tissue with an inflatable balloon. However, most of the balloons on the market are nonconforming, thus lose their shape when overinflated or squeezed. Thus, these balloons are less than an ideal solution, the prostate easily sliding off one side of the balloon or the other when in use.
RadiaDyne has provided an innovative solution to this problem, marketing a conforming rectal balloon that holds its shape even in the highly mobile environment of the rectum. This revolutionary new design has allowed the company to capture more than 90% of the prostate immobilizing rectal balloon market.
In more detail, the conforming immobilizing balloon of Ser. No. 11/966,544 et seq (all incorporated by reference herein) consists of three layers of material welded together at the edges, wherein the middle layer functions as a baffle and is also welded or glued to the upper layer. This weld or attachment point between the inner and upper layers provides a physical constraint against expansion on inflation or compression, and thus provides a groove or depression into which the prostate can be wedged during treatment.
Application Ser. No. 12/034,470 (incorporated by reference) provided a further improvement, allowing the distal surface to bulge on additional inflation, thus further wedging the seminal vesicles into position, and holding the balloon against expulsive forces. The distal bulge can be achieved in any number of ways, including making that portion of thinner material, making that portion of more elastomeric material. But, more simply, the distal bulge can be made by shifting the groove weld proximally, thus the greater amount of elastomeric material on the distal side will naturally stretch more. It is also possible to make a bulge or protrusion by welding on additional material, e.g., semicircular portion of material (like the finger on a glove), or by pre-shaping the balloon, such as by pressure/vacuum forming.
Both of these balloons were significant improvements over the prior art of non-conforming balloons, which were generally elastomeric and not physically constrained against bulging on compression, such that the prostate could easily slide away. The RadiaDyne conforming balloons allowed reduction of margins, reduction of dose to the rectum, reduction in margin surrounding the prostate, displacement of low lying bowel, reduction of dose related side effects, and the ability to escalate dose and increase the rate of local tumor control of prostate cancer. However, these balloons are also expensive to manufacture, each weld contributing to complexity and cost.
What is needed in the art are further improvements in balloon design that allow the manufacture of a shaped balloon, but is less expensive than the trilayer RadiaDyne balloons described above, yet is still a conforming balloon having a suitable shape.